1. Field of the Invention
The present invention relates to an apparatus for adjusting a rotor, and more specifically to an apparatus for adjusting an eccentricity at a coupling portion of the rotor, which can be applied to a rotating machine whose bearing characteristics vary markedly with increasing rotational speed.
2. Description of the Prior Art
In the case of an ordinary rotating machine such that a first rotor (e.g., a motor) and a second rotor (e.g., a pump shaft) are connected to each other via a coupling joint, it is necessary to estimate an eccentric quantity (decentering quantity) and an eccentric direction at the coupling joint in order to reduce an unbalanced force; that is, to adjust an eccentricity at the coupling joint of the rotor. The method of obtaining the above-mentioned eccentric quantity and direction can be classified roughly into a direct reading technique and a vibration vector analyzing technique.
In the former case, an inspector measures the shaft deflection quantity with the use of a gage as the measurement instrument under the condition that the rotor is being rotated at a low speed or rotated manually, and further calculates the adjustment quantity on the basis of the measured results.
On the other hand, in the latter case, a non-contact displacement sensor is used as the measurement instrument to extract the vibration vector components synchronizing with the rotational speed of the rotor, and a vibration vector at a zero rotational speed (N.sub.0) is obtained by approximating two vibration vectors (N.sub.1, N.sub.2), each composed of an amplitude and a phase as shown in FIG. 1(b), so as to be arranged on a mode circle of one degree of freedom under the assumption that the bearing characteristics are kept constant. The direction (the thick arrow direction in FIG. 1(b)) of an unbalance force (i.e., the eccentric direction) of the coupling joint of the rotor can be obtained on the basis of the direction of a tangent line described on the mode circle at this rotational speed N.sub.0. The eccentric direction to be adjusted is opposite to this thick arrow direction shown in FIG. 1(b). Further, the eccentric quantity can be estimated on the basis of a coefficient representative of the relationship between the amplitude and the eccentric quantity.
Further, in FIG. 1(a), two rotating shafts 1a and 1b are connected by two coupling joints 2a and 2b, and a displacement sensor 5 and a pulse sensor 7 (e.g., non-contact displacement meter) for detecting the rotational speed and a reference angular (marker) position of the rotating coupling joints are disposed a distance away from the coupling joints. Further, FIG. 1(b) indicates the relationship between the phase and the amplitude of vibration vectors N.sub.1 and N.sub.2 of the rotor shown in FIG. 1(a), in which .theta..sub.1 denotes an angle between a marker (see FIG. 1(a)) and the eccentric direction.
In the above-mentioned adjusting methods, however, when the bearing characteristics vary markedly with increasing rotational speed as with the case of a recirculating pump, the resonance frequency of the rotor also varies according to the rotational speed of the rotor as shown in FIG. 1(b). In addition, the vibration amplitude is subjected to the influences of dynamic vibration vector components dependent upon the rotational speed (e.g., the non-uniformity of the surface shape of a rotor) and of static vibration vector components not dependent upon the rotational speed. Therefore, in the prior art adjusting means established on the assumption that the bearing characteristics are constant, there exists a problem in that a precise estimation of the eccentric quantity and direction cannot be obtained and additionally a lot of time is inevitably required to adjust the eccentricity or decentering of the rotor.
Further, since dial gages have been so far used for the measurement instruments (as the displacement sensor 5 and the pulse sensor 7), vibration information can be obtained only when the rotor is rotating at a relatively low speed. In other words, it has been so far difficult to adjust the eccentricity of the rotor below a predetermined reference value, by predicting a vibration status at the rated rotational speed on the basis of the vibration conditions obtained at a plurality of different rotational speeds.